1. Field of the Invention
The present invention relates to a gas relief valve for a container and, more particularly, to a gas relief valve for a container, especially for an airtight closed container with contents generating gases during storage.
2. Description of the Related Art
For example, coffee beans or the like generate carbon gases upon roasting them. An amount of the carbon gases generated from coffee beans or the like become much larger particularly when they are pulverized to powders in a short time after they have been roasted and allowed to cool in a natural state. When powdery coffee beans or the like are packed in a container, such as a bag, box, can or the like, and the container is closed airtight or hermetically, the airtight closed container may become filled with carbon gases generated from the coffee powders or the like packed therein and the gases cause swelling the closed container with the contents such as coffee beans or the like filled therein. If the closed container continues swelling more and more, such continual swelling may eventually lead to a rupture of the closed container.
If containers which are filled with carbon gases generated from coffee powders or the like and which are swollen by the carbon gases filled therein are placed, for example, on counters of shops or the like, consumers may think of the coffee powders or beans contained in such swollen containers as time passing or deteriorating in quality.
Therefore, conventional containers in which to fill with contents such as, for example, coffee beans or powders, are provided with gas relief valves which are disposed, on the one hand, so as to remove carbon gases generated from the contents from the closed containers therethrough toward the outside before the carbon gases generated from contents packed therein and filled therein eventually lead to a rupture of the closed containers and, on the other hand, so as to suppress air from penetrating through the gas relief valve.
Some conventional gas relief valves are of a type having the function of discharging gases generated from contents filled in a closed container from the closed container to the outside while, at the same time, having the function as a check valve capable of suppressing air from penetrating into the container from the outside thereof. Such a gas relief valve comprises a ring shaped base plate made of a plastic material, a circular valve of a thin film made of a synthetic resin and having a shape substantially equal to the shape of the ring-shaped base plate, and a pair of left-hand and right-hand segments each having an arc shape substantially equal to the arc of the circular valve. An aperture of the ring-shaped base plate functions as a gas flow-out passage from the closed container when the gas relief valve is disposed on an outer surface of the container in which to fill with contents. The container is provided at its outer surface with an aperture having a small diameter through which to discharge the gases from the closed container to the outside. The gas relief valve is fused and attached integrally to the inner side wall surface of the container so as to let the aperture of its ring-shaped base plate coincide concentrically with the aperture of the container and the circular film valve is disposed on the ring-shaped base plate. Further, the pair of the left-hand and right-hand arc-shaped segments are fused and attached integrally on the circular film valve in a spatial relationship having a predetermined interval therebetween so as to allow each of the arc portions of the left-hand and right-hand arc-shaped segments to coincide with the corresponding arc portions of the circular film valve and to cause each of the chord portions of the arc-shaped segments to fail to close an upper portion of the aperture of the ring-shaped base plate. The bottom portions of the left-hand and right-hand arc-shaped segments are fused and attached integrally to the upper surface of the ring-shaped base plate so as to fail to close the aperture disposed in the ring-shaped base plate. As described hereinabove, the conventional gas relief valve is configured in such a structure that the opening disposed in the side wall of the container is enclosed concentrically with the aperture disposed in the ring-shaped base plate so as to allow gases filled in the container to pass through the apertures and to be discharged from the closed container, that the arc-shaped segments are disposed on the upper surface of the ring-shaped base plate so as to fail to close the aperture of the ring shaped base plate and so as to allow the spatial interval between the chords of the left-hand and right-hand arc-shaped segments to constitute a passage for the gases discharged through the closed container, and that the circular film valve is disposed on the arc-shaped segment so as to fail to close the gas-flow passage formed between the chords of the left-hand and right-hand arc-shaped segments.
With the arrangement of the structure of the conventional gas relief valve in the manner as described hereinabove, the aperture of the ring-shaped base plate disposed concentrically over the gas-flow opening of the side wall of the container is closed with the circular film valve disposed on the arc-shaped segment in a usual state, thereby causing the gases filled in the closed container to fail to be leak therefrom into the outside and, at the same time, preventing air from penetrating through the apertures of the ring-shaped base plate and the side wall of the container thereinto from the outside. On the other hand, as the gases are filled in the closed container and the gas pressure in the closed container is caused to elevate and reaches a predetermined pressure level, the portion of the circular film valve corresponding to or over the aperture of the ring-shaped base plate is caused to swell upward by the gases forced to pass through the apertures thereof, thereby forming a gas-flow gap between the upper surface of the ring shaped base plate and the bottom surface of the circular film valve and between the chords of the left-hand and right-hand arc-shaped segments, as well as eventually to be opened, thereby allowing the gases filled in the closed container to pass through the apertures of the closed container and the ring-shaped base plate and to be discharged through the gas-flow gap from the closed container to the outside.
As described hereinabove, the arrangement of the conventional gas relief valve can place the circular film valve over the gap portion between the chords of the left-hand and right-hand arc-shaped segments in usual instances in such a close state as capable of suppressing air from entering the closed container from the outside; however, in some cases, the extent of closeness may not be so airtight that the air cannot thoroughly penetrate into the gap between the ring-shaped base plate and the circular film valve because the risk still exists that there may be formed an opening so small yet enough to cause the air to enter the closed container through the opening from the outside of the container. If the air would enter the closed container with contents such as coffee beans, coffee powders or the like filled therein, the oxygen in the air may accelerate deterioration in the quality of the contents.